Many Electrical Engineers put "20kA @ 0.2s" ratings on the switchboards they are designing but they do not know how to calculate the rating or why they need to include the rating in their switchboard specification.

This is a sad and dangerous reality but even seasoned Electrical Engineers are not doing this calculation. It is either, they just copy whatever has been previously designed or worst, they are just doing guess works.

The purpose of this paper is to enable Electrical Engineers to calculate the Internal Arcing Fault Clearing Time and Peak Current Withstand of any switchboard they are assigned to design.

Any power system network (Figure 1) can be represented by a simplistic Thevenin’s equivalent circuit (Figure 2). Using the Thevenin’s equivalent circuit of the network, it will be very easy to calculate the fault current at any point of the…